| Mesoscale phenomena influence phytoplankton community composition, size class distribution, abundance and photosynthetic capacity, in turn determining food web structure. As this structure influences carbon sequestration in the oceans, mesoscale forcing affects carbon sequestration capacity. This study was conducted to characterize phytoplankton community structure and size class distribution based on HPLC-assisted chemotaxonomy of size fractionated samples from different environments in the eastern Caribbean under the influence of the Orinoco River plume and mesoscale eddies.;Little response to the effect of cyclonic and anticyclonic eddies in phytoplankton population and abundance was observed. However, a slight increase in pico and nanoplankton biomass was noted, with values higher in the cyclonic region than the anticyclonic region. Oligotrophic oceanic waters were found to be mostly dominated by pico and nanoplankton populations. However, increased river plume influence resulted in reduced proportional biomass of both nano and picoplankton and corresponding increase in microplankton.;Chemotaxonomic analyses of size fractionated samples show significant overlap of diagnostic pigments across the micro, nano and pico size spectrum indicating that size structure cannot be inferred solely by photosynthetic pigment identification. If specific size structure of phytoplanktonic populations is in question, sequential filtration using designated pore sizes coupled with HPLC is suggested. |
